Medical guide wires having miniature pressure sensors are well known. Such pressure guide wires typically have a pressure sensor located at the guide wire's distal end that is used to measure the pressure within a patient's artery. Electrical conductors which are connected to the pressure sensor are passed through the inside of the guide wire to a set of electrical contacts or sleeves located at the proximal end of the guide wire. The electrical contacts on the guide wire are mated to external monitoring equipment using an interface cable. The external monitoring equipment can provide pressure information to the attending physician that is useful in the diagnosis for example of an arterial occlusion. An example of such a pressure guide wire is described in U.S. Pat. No. 5,715,827, entitled "Ultra Miniature Sensor and Guide Wire Using The Same and Method".
In FIG. 1 there is shown a prior art pressure measuring system 100 comprising a guide wire 10 placed within a patient 12. The guide wire 10 is used with apparatus 20 that comprises rotary connector assembly 220 and a cable 214 that connects the rotary connector assembly 220 to an interface box 24. Connector 32 which is part of the rotary connector assembly 220 electrically interconnects with interface box connector 34.
Interface box 24 is connected by cable 26 to a pressure monitoring console 28, such as a WAVEMAP.TM. pressure monitoring instrument manufactured by EndoSonics, Inc., Rancho Cordova, Calif. Console 28 can display both proximal and distal pressure measurements as will has controls for calibrating the pressure wire 10 prior to its usage.
Referring now to FIG. 2, there is shown a more detailed view of the prior art pressure guide wire 10 coupled to a rotary connector assembly 220. As shown therein, pressure guide wire 10 can be manufactured utilizing the various constructions as shown and described in U.S. Pat. Nos. 5,163,445, 5,178,159 and 5,240,437. Guide wire 10 comprises a flexible elongate element 202 having a proximal and distal extremities 204 and 206 and which can be formed of suitable material such as stainless steel. The guide wire having an outside diameter for example of 0.018 inch or less and having a suitable wall thickness as for example, 0.001" to 0.002" and conventionally called a "hypotube" having a typical length of approximately 150-170 centimeters. A semiconductor pressure sensor 208 is located at the distal extremity of guide wire 10.
The proximal end of guide wire 10 is slid into a rotary connector 210 of the type described in U.S. Pat. Nos. 5,178,159 and 5,348,481 which is part of the rotary connector assembly 220. A torquer 230 is typically clipped-on by a physician distal to the rotary connector 210. Rotation of the torquer 230 causes rotation of guide wire 10 when used in connection with a catherization procedure in a manner well known to those skilled in the art. The proximal extremity 204 of the guide wire 10 is removably disposed within housing 212 of the type described in U.S. Pat. Nos. 5,178,159, 5,348,481 and 5,358,409. Located close to the distal extremity of guide wire 10 is a pressure sensor 208 which is used to measure pressure within a patient's blood vessels.
Electrical contacts located within housing 212 make electrical contact with electrically conductive sleeves (not shown in FIG. 2) located on the proximal extremity 204 of guide wire 10. The electrical contacts located in housing 212 allow for rotation of the guide wire while maintaining electrical contact with the conductive sleeves found in guide wire 10, these conductive sleeves are electrically coupled to pressure sensor 208. The electrical contacts in housing 212 are electrically connected to cable 214 that terminates in connector 32.
The connector 32 is connected to another mating connector 34 located on the interface box 24. Interface box 24 provides signal buffering and voltage level adjustments between guide wire 10 and pressure monitoring console 28. The electrically conductive sleeves 302, 304 and 306, which are located at the proximal extremity of guide wire 10, are shown in FIG. 3.
In FIG. 4 there is shown an electrical schematic representation of the pressure sensor 208 which comprises two variable resistors 402 and 404 whose resistance values vary with changes in pressure as is known in the art. Pressure sensor 208 can be a semiconductor having a diaphragm as is well known in the art. The two resistors 402 and 404 are connected to the three electrically conductive sleeves or bands 302, 304 and 306 located on the proximal extremity of guide wire 10 as shown.
FIG. 5 shows an exploded isometric view of the prior art rotary connector assembly 220 including rotartary connector 210 and housing 212. In operation, the proximal extremity of the flexible elongate member or pressure guide wire 10 is inserted into bore 501 with one hand while holding the rotary connector with the other hand. The nose piece 503 and the collar 504 are then pulled with fingers in a proximal direction against the force of the spring 508 to release the collet 502 and allow it to open. The guide wire 10 can then enter the bore 501 and pass through the inside of collet 502 and through bearing 510. The guide wire 10 is then pushed further in until conductive sleeve 302 is making electrical contact with contact member 546, conductive sleeve 304 is making electrical contact with contact member 544 and conductive sleeve 306 is making electrical contact with contact member 542.
Housing members 514 and 530 retain contacts 542, 544 and 546. A retaining ring 506, which is inserted through an opening in bearing 510, engages with and retains collet 502. Connector 32 provides an interconnection with the interface box 24 through a cable as shown in FIG. 1.
A problem with the above noted design is that sometimes as the guide wire 10 is being rotated, the contact resistance between electrically conductive sleeves 302, 304 and 306 located on the guide wire 21 and the corresponding electrical contacts located in housing 212 varies. This contact resistance variation is assumed to be caused by microscopic particles that get lodged between the pressure guide wire's conductive bands 302, 304 and 306 and the corresponding spring contacts 546, 544 and 542. This change in contact resistance causes an error in the pressure measurement as determined by pressure monitoring console 28, since this change in contact resistance affects the measurement of pressure sensor resistors 402 and 404.
An electrically equivalent circuit showing this change in contact resistance is shown in FIG. 8. Pressure sensor 208 is shown coupled to sleeve contacts (conductive bands) 302, 304 and 306 via electrical conductors. Sleeve contact 302 is shown coupled to contact 546, sleeve contact 304 is shown coupled to contact 544 and sleeve contact 306 is shown coupled to contact 542. Variable resistors 802, 804 and 806 represent the variable contact resistance caused by the rotating connector interface. The resistance of resistors 802, 804 and 806 vary as the pressure guide wire is rotated. As shown, contact resistance 802 is in series with sensor resistor 402 and contact resistance 806 is in series with sensor resistor 404 and thus any change in the contact resistance will affect the measurement of sensor 208. A need thus exists in the art for a solution that can minimize electrical interconnection problems as the one described above.